Understanding Automotive Air filter Testing: Auto Filters Categories and Performance Testing

Automotive filters are crucial in maintaining vehicles' overall performance and longevity. They are responsible for filtering various contaminants and impurities, ensuring clean air, oil, and fuel reach the engine and cabin. According to application, automotive filters can be divided into four categories: cabin, oil, fuel, and air intake. Their function is to filter airborne dust and contaminants, impurities in the fuel, and impurities in the engine oil.

This article provides an overview of the four main categories of automotive filters. Additionally, it explores the performance testing standards ISO sets for each filter type, shedding light on the evaluation criteria and test methods employed.

Cabin filters

Cabin filters are air filters and filter assemblies in automotive air conditioning systems, mainly used to filter fine particles (dust, powder, etc.) and gases (benzene, formaldehyde, SO2, etc.) invisible to the naked eye and remove foul odors to maintain the excellent air quality in the cabin. Thus reducing or even eliminating drivers' and passengers' allergies due to exposure to fine particles, such as tearing, itching, and other physical discomfort. In addition, cabin filters also effectively protect the car's air conditioning system, prevent the air conditioning system from mold and odor due to continuous exposure to air-containing impurities and maintain the working efficiency of heating or cooling.

Cabin filters are divided into single-effect filters and dual-effect filters. Single-effect filters are mainly used to filter particulate matter. In contrast, dual-effect filters can filter both particulate matter and motor vehicle exhaust due to the use of activated carbon filter material.

ISO 11155 Road vehicles - Air filters for passenger compartments is a standard on automotive air conditioning filters, divided into two parts: Part 1 Test for particle filtration, and Part 2 Test or gaseous filtration.

For particle filtration tests, efficiency tests use KCl or A2 dust aerosols for fractional efficiency and A2 dust aerosols for dust holding tests for gravimetric efficiency and dust holding capacity. In addition, the air volume vs. resistance needs to be tested.

The standard describes the test method, but no qualification criteria or classification method is stated. It is also mentioned that the filter performance in actual use may not match the ranking given by the test. Then, to better evaluate the filter, we recommended combining the laboratory test results with the air quality in the cabin monitored after the car is installed with the filter working under the same working conditions for a certain period and making a comprehensive classification of the filter.

For gaseous filtration tests, n-butane, toluene, and SO2 were used as test contaminants to test the adsorption performance (efficiency, capacity vs. time curve) and desorption performance of the filters.

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Oil filters

Oil filters are located in the engine lubrication system; upstream is the oil pump, and downstream is the engine needing lubrication of the parts. The primary function is to filter out the harmful impurities in the oil and supply the clean oil to the crankshaft, connecting rod, camshaft, piston ring, etc., which can play the role of lubrication, cooling, and cleaning, and prolong the service life of the parts.

Oil filters are divided into interchangeable, rotary, and centrifugal types according to their structure. The filter materials used are filter paper, felt, metal mesh, non-woven fabric, etc.

ISO 4548 Methods of test for full-flow lubricating oil filters for internal combustion engines series specifies the test methods for oil filters, and there are also JIS D1611 related standards. Test indicators include pressure drop-flow characteristics, high-pressure resistance test, high-temperature resistance characteristics test, cold start simulation test, static pressure breakage resistance test, particle counting method to determine the filtration efficiency and contaminant retention capacity test, etc.

Fuel filters

Fuel filters are filtration devices installed in the pipe between the fuel tank and the engine, mainly used to filter the impurities inside the fuel oil. Although the fuel quality has improved in the past few years, and there are fewer impurities, there are still impurities. Such as fuel in the transport process in the tanker off impurities, when refueling may be added, if used directly without filtering, may cause abnormal wear and tear on the engine.

There are two kinds of fuel filters in general, one is integrated with the fuel pump in the instrument, and the whole fuel filter is installed in the fuel tank; the filter of this structure is generally designed to be larger and has a larger capacity. The other is the external fuel filter, installed outside the fuel tank; the capacity of this filter is smaller.

Fuel filter test items include hot and cold alternating tests, pressure drop-flow characteristics tests, vibration fatigue tests, air pressure sealing tests, hydraulic pulse fatigue tests, etc.

Air intake filters

The role of the air intake filter is to filter out the impurities in the air entering the engine so that the impurities do not enter the cylinder and cause abnormal wear of the cylinder and shorten the engine's service life.

According to the application, it can be divided into two categories: automotive and industrial, and according to the structure, it can be divided into dry-type air cleaners and oil bath air cleaners. The air filter consists of two parts: filter element and housing. The main requirements are high filtration efficiency, low resistance to flow, and extended continuous use.

ISO 5011 Inlet air cleaning equipment for internal combustion engines and compressors - Performance testing specifies the performance test method for air intake filters. ISO 12103 A2 or A4 dust is used as the test aerosol for dry-type air filters to test the initial efficiency, total life efficiency, and capacity. In addition, restriction and differential pressure need to be tested. Oil bath air cleaners, oil carry-over tests, total life efficiency and capacity tests, and recovery tests are required. Look at our FEH Air Filter Test System-SC-7099.

Automotive filters are instrumental in maintaining vehicles' performance, durability, and air quality. Manufacturers and consumers must understand the different categories of filters, their functions, and the corresponding performance testing standards. Compliance with ISO standards ensures that filters meet the necessary efficiency and capacity requirements. By selecting and maintaining high-quality filters, vehicles can operate optimally while ensuring a clean and healthy driving environment.